The importance of electrostatic discharge (ESD) control in today's micro-electronics is already a well known fact and deserves the priority attention for all manufacturers of microchips. Much care is being taken in the manufacturing and handling of electrostatic discharge sensitive components with the objective to eliminate electrostatic discharge. People, equipments and materials have to be properly grounded to discharge harmful static charge that may reside on every people, equipments or materials.
A typical microchip test system in the market as shown in FIG. 1 consists of a test pin array 11, aligned at the correct position below the test socket, having the test pin array 12 penetrate through the test holes of the socket, rest on the appropriate test leads or test points 13 of the microchip and then start the microchip testing.
To reduce the amount of static charge generation of the microchip, it is common to find more and more ionizers are being used in its design to counter the threat of ESD. At the microchip test point, ionizer or ionizers are often installed at strategic location(s) to neutralise any static charge that may be lurking around the pick-up and shuttle area and those reside on the body of a microchip prior to testing.
While it is common to use such ionisation technique in the prevention of ESD, there are several shortcomings encountered in a typical semiconductor manufacturing environment.
Firstly, in a large scale implementation, it involves high cost of investment. Not only high investment is needed in the purchase of high reliability ionizers, it also incur high maintenance cost in the regular checks, periodical calibrations, repair (especially after warranty period) and many other hidden cost like record keeping, human resources required and the provision of production space, etc.
Secondly, they are performance limitations in the use of the ionizer(s) installed around at the testing point of a test handler.
a) Neutralisation time is too slow in today's high speed and high output test handlers. Static decay time of an ionizer drop significantly over time of usage due to unavoidable accumulation of ammonium compound substance deposited at the needle tips of the ionizer in the presence of natural nitrogen (N2) and moisture (H2O) in the air. Effectiveness of an air ionizer will lost if the sharpness of the needle tip is lost. Therefore cleaning of the needle tips regularly inside the test handler in order to maintain the reliable performance of an ionizer is extremely difficult and cumbersome in today's highly compact test handler design.
b) Certain level of skill is required for the productive use of ionizer like good understanding of the air flow characteristic, positioning, re-positioning after servicing and the influence of conductive material along the flow path of the ionized air, etc. All these will directly affect the performance of an ionizer. In reality, investment must be put in to train technician or engineer with proper skill & practical knowledge in order to handle air ionizers productively.
One skilled in the art may figure out an alternative solution based on the use of static dissipative material in the fabrication of the test socket to eliminate the ESD threat. However, such technique may raise the concern for the presence of leakage current which can affect the accuracy and reliability of the testing process in many today's highly ESD-sensitive microchips.
PCT application no. PCT/MY2009/00072 and patent application no. PI2010004975 offer alternative solutions replacing the use of ionizers in the combat against the ESD threat.
However, these solutions possess limitations in many real-life situations:
Firstly, many tiny microchip designs are difficult to fabricate due to too fine the geometry thus requires high investment in high precision tooling and expensive machine set-up.
Secondly, such difficulty further aggravated by the miniaturisation trend of the microchips in today's rapid product innovation towards smaller but higher performance devices.
Therefore, there is a need for further research and development work to eliminate or overcome the above shortcomings of the prior art.